1. Field of the Invention
The present invention relates to a milk pump device, a milking device comprising a milk pump device, and a method for displacing an amount of milk.
2. Description of the Related Art
A milk pump device can be used for displacing an amount of milk, for example for displacing an amount of milk collected in a milk glass to a further processing device or a milk storage. The milk pump device can be disposed in a milk line.
A milk pump device is known from British patent application no. GB2192673. GB2192673 discloses a milk pump device which is shown schematically in FIG. 1. The milk pump device (1) comprises a passage duct 10, a first one-way valve 11, a second one-way valve 12 and a membrane pump 20. The first and second one-way valves 11, 12 are included in the passage duct 10 and oriented in the same direction relative to each other. In this manner there is defined a flow direction through the passage duct in the passage direction of the one-way valves 11, 12. The flow direction is indicated by arrow A in FIG. 1. The use of a membrane pump has the advantage that no air is taken in, so that no or at least little air can enter the milk. A further advantage of the use of a membrane pump is that the milk is not damaged by the pumping and, for example, fat structures present in the milk are not damaged. The use most other types of pumps may, on the contrary, lead to damage of milk fat structures or to undesirable mixing of air and milk.
The membrane pump 20 is positioned between the first one-way valve 11 and the second one-way valve 12. The membrane pump 20 is also called a membrane compressor or diaphragm compressor.
The membrane pump 20 comprises a pump chamber 21, with a membrane 22 included therein. The membrane 22 divides the pump chamber 21 into a first space 24 and a second space 25. The membrane 22 prevents transport of gas and/or liquid between the first space 24 and the second space 25. Owing to the fact that the membrane 22 has a certain degree of flexibility, the volumes of the first space 24 and the second space 25 may vary relative to each other.
The first space 24 is, via an opening 23, closably connected with a (high pressure) supply (not shown), for example compressed air or a pump. The second space 25 is in connection with the passage duct 10.
The functioning of the membrane pump 20 will be described briefly hereinafter. There is started from an initial position of the membrane 22 (first position) in which the volume of the first space 24 is almost maximal and the volume of the second space 25 is almost minimal.
If the supply of high pressure gas via opening 23 is stopped, milk flows into the second space 25 via the first one-way valve 11 and presses the membrane 22 away from the first position so that the volume of the first space 24 is reduced. The membrane 22 then assumes a second position.
Under the influence of pressure or gravitational force, the milk can flow into the second space 25 of the pump chamber 21. This can also take place or be promoted by sucking air, via opening 23 (or another not shown opening), from the first space 24, for example by means of a (vacuum)pump (not shown). The membrane 22 will now be forced into the second position, in which the volume of the first space 24 is almost minimal and the volume of the second space 25 is almost maximal.
The first space 24 can subsequently be filled via opening 23, so that the volume of the first space 24 is increased and the volume of the second space 25 is reduced. The membrane 22 then moves from the second position (shown by a solid line in FIG. 1), to the first position (shown by a dotted line in FIG. 1). The milk present in the second space 25 will be discharged through the passage duct 10 in the flow direction A. The above-described cycle results in displacement of the milk through the passage duct 10 in the flow direction A.
The membrane 22 passing once through a cycle, for example from the first position to the second position and back to the first position, is called a pumping stroke.
In the above-described example of a membrane pump 20, a pumping stroke is defined, in which the pump displaces a fixed volume of milk per pumping stroke or per cycle.
There may be performed a number of pumping strokes in order to displace an amount of milk in the flow direction A.
The milk pump device can be used for displacing an amount of milk which has, for example, just been obtained from a dairy animal. In this case it is of importance that the amount of milk obtained is measured with a certain degree of accuracy. In this manner it is possible, for example, to record the amount of milk obtained per dairy animal or the total amount of milk obtained from a number of dairy animals can be determined. This can take place by measuring the amount of milk displaced. However, a disadvantage of the flexible membrane is that by means of such a membrane pump the displaced volume of a partial or residual pumping stroke cannot be identified (accurately).
The present invention aims at providing a milk pump device of the described type by means of which the amount of displaced milk can be measured relatively accurately.